Interpretive Summary: An important question in evolutionary biology asks why genetic variation is maintained in populations of animals despite some individuals being selected as mates and thus reproducing more frequently than other individuals. This research addressed the hypothesis that genetic variation is maintained to allow at least some portions of the population to cope with varying environments. We measured the success of a honey bee pest, the lesser wax moth, as the ability of male moths (specifically, some features of their ultrasonic courtship calling songs) to attract female moths, and the developmental attributes of the offspring coming from successful pairings. Responses of females were measured as the males called in environments that varied in temperature, food availability and larval rearing density. Genetic components involved parental groups obtained from two geographic areas (Maryland and Louisiana) and the offspring families derived from these parents. Genetic lines varied in their success under the different environments. About half of the lines had relatively uniform responses for most traits in all environments. The other lines had responses that varied with changing environments. This mixture of responses of the genetic lines supports the hypothesis that environmental constraints help maintain genetic variance in this species.

Technical Abstract:
Significant additive genetic variance often occurs for male advertisement traits in spite of the directional selection imposed by female choice, a problem generally known in evolutionary biology as the lek paradox. One hypothesis, which has limited support from recent studies, for the resolution of this paradox is the role of genotype × environment interaction in which no one genotype exhibits the superior performance in all environments—a crossover of reaction norms. However, these studies have not characterized the actual variation of reaction norms present in natural populations, and the extent to which crossover maintains genetic variance remains unknown. Here, we present a study of genotype × environment interaction for the male calling song in populations of Achroia grisella (Lepidoptera: Pyralidae; lesser waxmoth).We report significant variance among reaction norms for male calling song in two North American populations of A. grisella as measured along temperature, food availability, and density gradients, and there is a relatively high incidence of crossover of the temperature reaction norms. This range of reaction norm variants and their crossover may reflect the co-occurrence of plastic and canalized genotypes, and we argue that the different responses of these variants along environmental gradients may contribute toward the maintenance of genetic variance for male song.